Thermodynamics

Thermodynamics studies heat, work, temperature, energy, and the rules governing their transformations. Its laws constrain how energy moves and how physical systems change.

Thermodynamic system: A chosen quantity of matter or region of space, separated from its surroundings by a real or imagined boundary. Thermodynamic laws describe changes in a system and its exchanges with surroundings.
Zeroth law of thermodynamics: The law stating that systems separately in thermal equilibrium with a third system are in equilibrium with each other. It makes temperature a consistent way to compare thermal states.
Carnot cycle: An ideal reversible cycle of two isothermal and two adiabatic processes between two heat reservoirs. It establishes the maximum efficiency possible for a heat engine operating between fixed temperatures.
Sadi Carnot: A French engineer whose 1824 analysis of ideal heat engines established a limit on their efficiency. His reasoning about reversible engines helped found classical thermodynamics.
Statistical thermodynamics: A formulation of thermodynamics that uses statistical ensembles to calculate macroscopic properties from microscopic states. It supplies microscopic predictions alongside the classical laws.
State variable: A measurable property whose value describes the state of a physical system. Pressure, volume, and temperature specify thermodynamic states.
First law of thermodynamics: The principle that a system's energy change equals energy transferred as heat and work, with signs set by convention. It formalizes conservation of energy in thermodynamic transformations.
Heat engine: A device that converts heat absorbed from a hot source partly into work while rejecting remaining heat to a colder sink. Its performance is bounded by thermodynamic laws.
James Prescott Joule: An English physicist whose experiments established the mechanical equivalent of heat. His measurements helped show that heat and work are forms of energy transfer.
Kinetic theory of gases: A model that explains gas properties through the motions and collisions of molecules. It offers a microscopic account of pressure and temperature for gases.

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